What role does the diaphragm play in ventilation?

• A. It filters air before it enters the lungs
• B. It contracts and relaxes to change thoracic pressure
• C. It stores air for later use
• D. It controls heart rate

Answer: (B)

The diaphragm plays a crucial role in ventilation by contracting and relaxing to change thoracic pressure, which facilitates airflow into and out of the lungs. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity. This increase in volume leads to a decrease in pressure within the thoracic cavity relative to atmospheric pressure, causing air to flow into the lungs—a process known as inhalation. Conversely, when the diaphragm relaxes, it moves upward, decreasing the volume of the thoracic cavity and increasing the pressure, which forces air out of the lungs during exhalation. This mechanism of pressure change is fundamental to the process of breathing, making it essential for gas exchange in the respiratory system. The diaphragm's contraction and relaxation directly influence the mechanics of ventilation, allowing for effective respiration.